1. Field of the Invention
The present invention relates to a double meshing-type silent chain capable of meshing with sprockets located inside and outside the chain and to a sprocket for meshing with the chain along the outer circumference thereof.
2. Description of the Related Art
Conventionally, in some cases, a double-meshing-type silent chain capable of meshing with sprockets or toothed pulleys which are mounted on respective driven shafts located inside and outside the chain is used as a timing chain for transmitting rotational motion from the crankshaft of an engine to the cam-shaft of the engine or to the shaft of an auxiliary device such as an oil pump. A double-meshing-type silent chain is employed when driven shafts located inside and outside the chain must be rotated in opposite directions.
FIG. 10 shows a conventional double-meshing-type silent chain. In FIG. 10, an endless chain A1 meshes with a sprocket A2 located inside the chain A1 as well as with a toothed pulley A3 located outside the chain A1.
In the chain A1, links, each composed of three kinds of link plates having different shapes, are connected by pins A4. Specifically, guide link plates A5 are disposed at the widthwise outermost sides of the chain A1 as well as alternately along the longitudinal direction of the chain A1. As shown in FIG. 11, the guide link plate A5 has a straight edge portion a formed at the inner circumferential side of the chain A1 and two small meshing teeth b which are formed at the outer circumferential side of the chain A1 to be located at longitudinally opposite end portions of the guide link plate 5. The small meshing teeth b mesh with the toothed pulley A3.
A link plate A6 is pin-connected with adjacent guide link plates A5 at opposite end portions thereof such that the link plate A6 is in contact with inside faces of the guide link plates A5. The link plate A6 has two meshing teeth c formed at the inner circumferential side of the chain A1 so as to mesh with the sprocket A2, as well as two small meshing teeth b formed at the outer circumferential side of the chain A1 so as to mesh with the toothed pulley A3.
Plates A7 and A8 each have two meshing teeth c formed at the inner circumferential side of the chain A1 so as to mesh with the sprocket A2, as well as a flat back face d formed opposite to the meshing teeth c.
Notably, the meshing teeth c formed at the inner circumferential side of the chain A1 and the teeth of the sprocket A2, which mesh with the meshing teeth c, employ a standard tooth profile. By contrast, the meshing teeth b formed at the outer circumferential side of the chain A1 and the teeth of the toothed pulley A3, which mesh with the meshing teeth b, employ a non-standard tooth profile.
The above conventional double-meshing-type silent chain employs three kinds of link plates having different shapes. Thus, in a step of manufacturing plates, link plate dies corresponding to the different link plate shapes must be used. Also, in an assembling step, a large number of kinds of component parts must be handled and controlled. As a result, manufacturing cost is high.
Also, since the profile of the meshing teeth formed at the outer circumferential side of the chain is smaller than the standard tooth profile, when a large load torque acts on the toothed pulley located outside the chain, the toothed pulley disengages from the chain and slips along the chain. Thus, a maximum torque that can be transmitted to the toothed pulley is smaller than that which can be transmitted to the sprocket located inside the chain. This significantly limits the selection of a device to be driven through engagement with the outer circumference side of the chain.
Further, the guide link plate has no meshing teeth at the inner circumferential side of the chain, but instead has the straight edge portion at the inner circumferential side of the chain. Consequently, the guide link plate is relatively heavy, causing an increase in the weight of the entire chain. This causes an increase in impact energy generated due to meshing engagement between the chain and the sprocket or between the chain and the toothed pulley when the chain travels, resulting in an increase in working noise.
Also, a heavy chain weight causes an increase in tension derived from a centrifugal force produced when the chain travels, accelerating wear of a shoe surface of a chain guide or the like as well as elongation of the chain. Particularly, when such a double-meshing-type silent chain is used as a timing chain for an engine, timing drive of the engine may be adversely effected.
An object of the present invention is to provide a double-meshing-type silent chain which solves the above-mentioned problems involved in the prior art, enables a reduction in manufacturing cost through improvement of productivity, and enables transmission of a strong driving force between the chain and a sprocket meshed with the chain along the outer circumference thereof.
Another object of the present invention is to provide a sprocket. for meshing with the double-meshing-type silent chain along the outer circumference thereof and for serving as a chain guide to suppress chain vibration.
To achieve the above object, the present invention provides a double-meshing-type silent chain comprising link plates having the identical side profile. Each link plate has two meshing teeth and a flat back face formed opposite to the meshing teeth. Two kinds of links are alternately arranged in the longitudinal direction of the chain, while the adjacent links are connected by pins. In one kind of link, an odd number of the link plates are disposed in the width direction of the chain. In the other kind of link, an even number of the link plates are disposed in the width direction of the chain. In each link, the link plates are oriented such that the meshing teeth of link plates located at widthwise opposite ends project outwardly with respect to the chain and the meshing teeth of the remaining link plates project inwardly with respect to the chain.
In the double-meshing-type silent chain of the present invention, all of the link plates have the identical side profile. Also, the outermost link plates of each link are oriented such that their meshing teeth project outwardly with respect to the chain. Thus, these outwardly projecting meshing teeth are meshed with a sprocket disposed outside the chain to thereby transmit power between the chain and the sprocket.
In each link, all the link plates except the outermost link plates are oriented such that the meshing teeth project inwardly with respect to the chain. These inwardly projecting meshing teeth are meshed with a sprocket disposed inside the chain to thereby transmit power between the chain and the sprocket.
Since all of the link plates have the identical side profile, the link plates can be manufactured through use of a single kind of link plate die. As compared to the case of a conventional chain of this kind composed of link plates having a plurality of side profiles, man-hours required for control of component parts can be reduced, and erroneous assembly can be prevented, thereby greatly improving productivity.
In contrast to the case of a conventional silent chain, large heavy guide plates having no teeth are not used, thereby reducing the weight of the entire chain.
Further, since meshing teeth which project outwardly with respect to the chain are profiled similarly to those which project inwardly with respect to the chain, there can be increased a torque that can be transmitted between the chain and a sprocket disposed outside the chain.
Preferably, the double-meshing-type silent chain of the present invention is such that, in each link, the meshing teeth of some link plates oriented in one direction project beyond the back faces of the remaining link plates oriented in an opposite direction.
In this case, the shoe face of a chain guide or that of a tensioner lever can be brought into slidable contact with the back faces of the plates oriented outwardly with respect to the chain, while the opposite side faces of the shoe are guided along the inside faces of the meshing teeth of the opposed outermost link plates, which meshing teeth project outwardly beyond the plate back faces.
The present invention provides a first-type sprocket for meshing with a double-meshing-type silent chain along the outer circumference thereof, wherein a plate support face is formed in each of sprocket teeth so as to support back faces of link plates which are oriented outwardly with respect to the chain, during the sprocket meshing with link plates whose meshing teeth are oriented outwardly with respect to the chain.
In the first-type sprocket, power transmission is achieved through engagement with the meshing teeth of the outermost link plates in each link. Also, the plate support face formed in each sprocket tooth abuts back faces of link plates which are oriented outwardly with respect to the chain, to thereby partially bear a reaction force of the running chain imposed on sprocket teeth and thus improve sprocket durability. Further, the plate support faces serve as a chain guide for guiding the back faces of link plates to thereby suppress chain vibration.
Since an existing standard sprocket can be used as the first-type sprocket by machining tip portions of sprocket teeth to form the plate support face in each sprocket tooth, the first-type sprocket can be manufactured at low cost and can be used with the double-meshing-type silent chain of the present invention.
The present invention provides a second-type sprocket for meshing with a double-meshing-type silent chain along the outer circumference thereof, comprising a plate-back-face support element and two meshing elements. The plate-back-face support element has a cylindrical surface that abuts flat back faces of link plates which are oriented outwardly with respect to the chain. The meshing elements are integrally coupled with the plate-back-face support element such that the plate-back-face support element is interposed between the meshing elements. Meshing teeth are formed on the circumferences of the meshing elements concentrically with the cylindrical surface of the plate-back-face support element so that the meshing elements can mesh with link plates whose meshing teeth project outwardly with respect to the chain.
In the second-type sprocket, the two meshing elements have meshing teeth which are formed on the circumferences and which are profiled so as to completely mesh with outwardly projecting meshing teeth of the chain. Therefore, when the second-type sprocket is meshed with the outer circumferential side of the double-meshing-type silent chain of the present invention, a large torque can be transmitted therebetween.
Also, in the second-type sprocket, the plate-back-face support element has a continuous cylindrical surface for contact with back faces of link plates. The continuous cylindrical profile establishes continuous and smooth contact with the back faces, thereby significantly suppressing chain vibration and partially bearing a reaction force of the running chain imposed on sprocket teeth to thereby lessen sprocket teeth load. Thus, sprocket durability can be improved.